Description will be given of a concrete construction of a conventional radiation tomography apparatus. As illustrated in FIG. 7, a conventional radiation tomography apparatus 50 includes a top board 52 configured to support a subject M placed thereon, and a detector ring 62 configured to detect annihilation radiation pairs. The detector ring 62 has an opening into which the subject M is insertable together with the top board 52.
When the conventional radiation tomography apparatus 50 is used to determine radiopharmaceutical distribution in the subject M, the subject M is moved inside the opening of the detector ring 62. Thereafter, positions of occurrence of annihilation radiation-pairs emitted from the subject M are imaged, whereby a radiation tomographic image is obtained. Such a radiation tomography apparatus is referred to as a PET (positron emission tomography) apparatus. The PET apparatus identifies occurrence status of the annihilation radiation-pairs by counting the number of coincidence events, thereby obtaining a tomographic image. Here, the coincidence event represents detection of two rays of radiation at different positions in the detector ring 62.
The detector ring 62 has radiation detectors arranged annularly. Consequently, an annihilation radiation-pair is detected coincidentally with different radiation detectors. Each of the radiation detectors cannot determine whether or not the detected radiation is derived from the annihilation radiation-pair. Accordingly, the conventional construction transmits the detected data received from the radiation detectors to one substrate 63. See FIG. 8. The substrate 63 receives the detected data from all the radiation detectors constituting the detector ring 62. The substrate 63 finds two pieces of the detected data having coincident detection time. In such manner, one coincidence event is to be found.
The substrate 63 successively finds coincidence events through checking the detected data, and counts the number of coincidence events. The number of coincidence events obtained in such manner is used for generating a tomographic image. See, for example, Japanese Patent Publication No. 2008-190901A.